In recent years, there has been an increased use of fuel, e.g. heavy oil, containing sulphur. This constitutes a serious problem in terms of a public nuisance, due to the presence of harmful sulphur oxides, i.e. SO.sub.2 and SO.sub.3, in the exhaust gases which arise from the combustion of such sulphur in the fuel, e.g., in electric power stations and other industrial plants. The elimination of such sulphur oxides is very important from the standpoint of preventing this public nuisance, and there have heretofore been proposed a variety of measures therefor. However, none of these proposals are entirely satisfactory.
Such proposed measures are generally classified in two categories: the wet method and the dry method. The former is based on the principle of wasing out any sulphur oxides in a gas, using water or other solvents. The drawbacks of this method are that it must be carried out at a low temperature, and the exhaust gas after washing is at a low temperature. Consequently there is a large amount of condensed water vapor in the waste gas, with the result that the waste gas does not disperse efficiently when discharged from an exhaust duct into the open atmosphere.
On the other hand, the dry method uses various substances as physical and chemical sorbents, including activated carbon in some cases. This method has the advantage that the waste gas is discharged at a comparatively high temperature thus avoiding the difficulties mentioned above. However, it is not possible to treat large quantities of gas in this way due to the considerable expense involved in replenishing or regenerating the sorbent.